Bacteria are grown in a medium containing [¹⁵N]H₄Cl for a number of generations so that all of the DNA is made of fully 'heavy' DNA. The bacteria are moved to a new medium and grown in [¹⁴N]H₄Cl so that all subsequent new DNA will be 'light.' After one generation time, what does the DNA look like? A)All of the DNA is made of two 'light' strands. B)All of the DNA is made of two 'heavy' strands. C)All of the DNA is made of one 'heavy' strand and one 'light' strand. D)Each strand is made of a mixture of 'heavy' and 'light' DNA, with each strand being between 75% and 100% 'light.' E)Half of the DNA is made of two 'light' strands and half is made of two 'heavy' strands.

Question

Quizplus · Accepted Answer

The initial generations in the medium with heavy DNA resulted in all DNA being heavy. However, after moving to the new medium with light DNA, the newly synthesized strands will be light while the original strands will still be heavy. Therefore, the resulting DNA after one generation will be a mixture of heavy and light strands, with each strand being a combination of one heavy and one light strand, resulting in all the DNA being made of one heavy and one light strand. This is referred to as semi-conservative replication.

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